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Oracle Tips by Burleson

Disk I/O Tuning

Chapter 3: SCSI Tuning Under AIX

For non-IBM devices, it is sometimes required to modify AIX default queue-limit values to ensure highest performance rather than use those that have been chosen to handle the worst possible case.  Let's look at situations in which the defaults should be changed and the IBM recommended new values.

AIX SCSI Settings With a Non-IBM Disk Drive

The default settings for AIX for IBM disk drives for the number of requests that can be outstanding at any given time is 3 (8 for SSA).  This value has no direct interface for changing it.  The default hardware queue depth for non-IBM disk drives is a very performance killing 1.  It behooves you to change the setting for Non-IBM drives if they can accept multiple commands (most modern drives can), so you can get the maximum performance from those drives.  For example, you can display the default characteristics of a non-IBM disk drive with the lsattr command:

# lsattr -D -c disk -s scsi -t osdisk

pvid          none Physical volume identifier      False
clr_q         no   Device CLEARS its Queue on error
q_err         yes  Use QERR bit
q_type        simple Queuing TYPE
queue_depth   3    Queue DEPTH
reassign_to   120  REASSIGN time out value
rw_timeout    30   READ/WRITE time out value
start_timeout 60   START unit time out value

You should use the AIX provided interface, SMIT to change the disk parameters as required.  SMIT allows for
 

The above text is an excerpt from:

Oracle Disk I/O Tuning
Disk IO Performance & Optimization for Oracle Databases
ISBN 0-9745993-4-4 

by Mike Ault
 


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Burleson Oracle Consulting offers Senior Oracle consultants which are available for all areas of Oracle support.  Common Oracle consulting support activities include short-term Oracle tuning, Oracle database troubleshooting, Oracle9i and Oracle10g migration, Oracle9iAS App Server consulting, Oracle design reviews and Oracle requirements evaluation support. Oracle support and Oracle consulting services are priced by the hour, so you only pay for what you need. These one-time Oracle consulting services commonly include:

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